SnowLoadCheck

LaSalle County, IL Roof Snow Load - 20 psf

LaSalle County, IL: your roof's ASCE 7 snow number, in plain English

Moderate
20 psf

LaSalle County's roofs are built to hold 20 psf of snow, the ASCE 7-22 figure a permit reviewer checks first. The physics-based figure alone would be 14 psf, but ASCE 7's own low-slope minimum (§7.3.4) sets a floor of 20 psf for flat and low-pitch roofs here, which is the number that actually governs.

In depth, not weight: that's roughly 44 inches of fresh, light snow, 16 inches of old, settled snow, or as little as 4 inches of solid ice - snow that heavy is rare here but ice from a freeze-thaw cycle adds up far faster than the depth suggests. This is a meaningful design load - most modern-code homes handle it fine, though an addition, a carport or a flat-roofed section can be a weak spot.

LaSalle County in numbers

LaSalle County by the numbers

Nationally that's #641 out of 2,758 rated counties, the top 23%; within Illinois alone, LaSalle County ranks #17 of 102. That's 0.7 psf above Illinois's own county-average design load of 19.3 psf.

LaSalle County, FIPS 17099, is home to 108,390 people near 41.3433°N 88.8859°W. Its 20 psf ground snow load figure is the map value; 20 psf is what a roof is actually designed for.

LaSalle County's snowfall, most winters

23.7 in. a year: that's LaSalle County's NOAA 1991-2020 snowfall normal, measured at OTTAWA 5SW, IL US (1.6 mi away). See the density guide.

Before you rely on LaSalle County's number

Treat the LaSalle County figure as a starting point, not a final answer: it assumes standard occupancy, a heated structure and a moderately sheltered site, per ASCE 7-22's own defaults. Exposed terrain, an unheated building or a steeper roof all shift the real number.

For a real application, skip the county number and go straight to the ASCE 7 Hazard Tool - enter your coordinates and it returns a site-specific figure a plan reviewer will recognize. (How this figure is calculated.)